This invention relates in general to test equipment for electronic devices. More specifically, it relates to a storage unit that continuously receives, holds, and then discharges integrated circuits (IC's) to a tester.
In the manufacture and use of IC's it is necessary to test them reliably and rapidly. Many IC's must be heated uniformly to a preselected temperature prior to testing to simulate actual operating conditions. Therefore modern high speed testing equipment must include a time delay storage device that can heat the IC's to a preselected temperature during a time interval. The storage unit must also be able (1) to receive the IC's from "tubes" or "sticks" where they are stored in an end-to-end linear array (2) to discharge them quickly and reliably at an input to the testing area, and (3) to store any standard size IC with little or no interruption of the testing process and not degradation of the performance of the storage unit.
One known approach to time-delay storage is to load the IC's from a tube into one or more holding rails that are mounted generally parallel to one another and in a circle. This assembly rotates about the common axis of rotation located at the center of the circle and inclined with respect to the ground. In this prior art arrangement, the IC's are loaded onto the rails at one angular position and discharged at another. The time delay and heating occurs as the rails rotate between these positions. The IC's held in a rail are loosely loaded, that is, there is some "play" or clearance in the line. This characteristic is important in order to have the IC's slide freely along the rail and to accommodate IC's having different sizes.
This "rotating rail" approach, however, has not found wide acceptance. A principal reason is that as the rails rotate, the IC's stored on the rails shift their positions with respect to one another so that at least some of them usually become wedged against the guide surfaces of the rails. Once the line of IC's on a rail is thus jammed, it will not discharge the IC's "behind" the jam point. This interrupts the flow of IC's to the tester and reduces the operating speed of the entire tester. (IC's have a generally rectangular, box-like body usually formed of a ceramic (or plastic) with leads emerging from opposite side faces of the body and projecting generally in a direction normal to one face of the body.)
Another approach to the storage problem has been to feed the IC's onto a carousel that extends generally in a horizontal plane. The IC's are arrayed about the periphery of the carousel. The carousel rotates each IC from a loading point to a discharge point. During this rotation the IC's are in a heated environment that brings them up to the desired testing temperature. The Type 1157 HL tester manufactured by Daymarc Corporation, the assignee of the present application, utilizes this carousel approach. While the carousel works well, it requires precise and costly machining of numerous parts. In addition, the close tolerances of peripheral openings on the carousel can become misaligned in normal handling resulting in the malfunctioning of some of the IC holding positions on the carousel. Further, the horizontal orientation of the carousel can place constraints on the type of testing circuitry that can be used or on the spacing between the circuitry and the site where the IC's are connected to the circuitry and tested. These geometrical considerations can be quite important since many IC's are very high speed devices and the quality and reliability of the test depends on placing the test circuitry extremely close to the IC being tested. However, alternate arrangements using a horizontal carousel which do not restrict the tester are possible.
It is therefore a principal object of the present invention to provide a storage unit for IC's that reliably and rapidly loads and unloads a line of loosely-loaded IC's to feed a tester.
Another object of this invention is to provide a storage unit that has a favorable cost of manufacture as compared to carousel type IC storage units presently in use.
Yet another object is to provide an IC storage unit with the foregoing advantages that can receive, store and discharge IC's having any of the standard sizes without jams.
A further object is to provide a storage unit with the foregoing advantages that is comparatively rugged and has no sensitive adjustments or components that are readily damaged in normal handling.
Still another object is to provide an IC storage unit that is compact and mates with a tester in a manner that does not limit the type of test circuitry or its positioning with respect to the tester.